This section provides background information related generally to the present disclosure and is not necessarily prior art.
Noise heard by occupants riding in the passenger cabin of an automotive vehicle comes from various sources including the vehicle's powertrain, the road, and window buffeting. The window buffeting noise is particularly disturbing, and unlike the other types of noise, is encountered more often in newer vehicles. Window buffeting, also referred to as wind buffeting, Helmholz resonance, or the helicopter effect, occurs when one of the windows of the vehicle is lowered to create an opening to the cabin and allow air to enter the cabin while the vehicle is in motion. Window buffeting is caused by a shear layer established at an upstream edge of the window opening to the cabin. Disturbances are shed from this location and travel along the side of the vehicle. When the disturbances reach the rear edge of the window opening, a pressure wave is generated that propagates both inside and outside the cabin. Outside the vehicle, the pressure wave propagates both forward and backward. When the forward traveling wave reaches the front edge of the window opening, it triggers another disturbance that moves back toward the rear edge of the window opening. This process is repeated many times each second and causes the shear layer to develop a characteristic buffeting frequency. The buffeting frequency and resulting noise depends on many factors which may include, for example, the size and shape of the vehicle, the position of the lowered window, the geometry of the opening created by the lowered window, the volume of the vehicle cabin, the speed of the vehicle, the relative air flow direction and speed over the vehicle body, and the temperature, pressure and density of the surrounding air. While the buffeting frequency may be below a range that can be heard by humans, the buffeting effect can still be felt by the vehicle occupants as a pulsating wind force. In addition, the associated vibration in the vehicle structure may cause undesirable resonator effects.
The window buffeting noise and associated vibrations are typically distracting and annoying to occupants riding in the vehicle. Typically, the driver eliminates the window buffeting noise and vibration by immediately closing the window, which is not ideal and may be hazardous since some of the driver's attention is taken away from the road and surrounding traffic. Although window buffeting noise is easy to measure with a microphone, the pressure waves causing the noise are difficult to analyze. Accordingly, there remains a need for an improved apparatus and method for alleviating window buffeting noise and vibrations, particularly in motor vehicle applications.